Recently along with increase in density, integration, output and others of electronic parts such as semiconductor elements, measures to the heat released from these electronic parts are becoming more important and there is thus increasing interest on metal-base substrates superior in heat dissipation efficiency. In particular, since LEDs, which are used in illumination application, generate much heat, metal-based circuit boards have been used for LEDs for improvement in reliability and life. Thus, there is a need for methods for efficiently manufacturing a metal-base substrate and a circuit board, which are superior in quality and inexpensive.
Hitherto proposed was a method of manufacturing a metal-based circuit board by forming an insulating layer of crosslinked transparent silicone by coating a crosslinkable silicone on a metal base of aluminum or an aluminum alloy and forming a circuit directly thereon (see, for example, Patent Document 1). Also proposed was a method of manufacturing a metal-based circuit board by laminating and integrating an adhesion sheet of an insulative resin and an inorganic filler and additionally a metal foil on a metal board in that order (see, for example, Patent Document 2).